Imaging apparatus and imaging method

ABSTRACT

An imaging apparatus includes an imager with an imaging optical system to having an object-side hypercentric property, an illuminator with a plurality of illumination optical systems having mutually different exit pupil positions and a mover for relatively moving these with respect to a well plate. Imaging is performed simultaneously with stroboscopic illumination when the imager is located at a predetermined imaging position, and illumination optical systems are switched according to the imaging position.

CROSS REFERENCE TO RELATED APPLICATION

The disclosure of Japanese Patent Applications enumerated belowincluding specification, drawings and claims is incorporated herein byreference in its entirety: No. 2016-39258 filed Mar. 1, 2016.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a technique for imaging raw samples carriedtogether with liquid in a sample container and particularly relates tothe illumination of the raw samples.

2. Description of the Related Art

In medical and bioscience experiments, liquid or gel-like fluid (e.g.culture fluid, culture medium or the like) is poured into each well of aplate-like sample container (e.g. called a microplate, a microtiterplate or the like) on which a multitude of recesses, for example, alsocalled wells are arranged, and cells and the like cultured here areobserved and measured as samples. In recent years, samples have beenimaged and converted into data by a CCD camera or the like, and variousimage processing techniques have been applied to this image data forobservation and analysis.

In such an imaging apparatus, there is a problem that illumination lightis refracted by the meniscus of a liquid surface and the brightness ofan image becomes insufficient particularly at peripheral edge parts ofthe wells. To deal with this problem, in a technique described in JP2015-118036A previously disclosed by the applicant of this application,an imaging optical system has an object-side hypercentric property,whereby light having a propagation direction bent in a direction awayfrom an optical axis by refraction can be efficiently collected.

SUMMARY OF THE INVENTION

To observe finer structures, it is considered to set a higher imagingmagnification of the imaging optical system. Further, the wells usedcome in various sizes. In these cases, there are cases where an areawith the influence of the meniscus is included in an imaging field ofview and cases where such an area is not included, particularly if animaging field of view becomes smaller than one well. When the areawithout the influence of the meniscus is imaged, a light quantity isreduced in a peripheral edge part of the imaging field of view inimaging using the imaging optical system described above and aneffective imaging field of view may become narrower.

This invention was developed in view of the above problem and aims toprovide a technique capable of obtaining an image with good imagequality by suppressing the influence of meniscus in a technique forimaging raw samples carried together with liquid in a sample container.

According to a first aspect of the disclosure, there is provided animaging apparatus that images a raw sample as an imaging object carriedtogether with liquid in a sample container with a bottom surface havingoptical transparency. The apparatus comprises: a holder that holds thesample container; an imaging optical system, arranged to face the samplecontainer held by the holder, that has an object-side hypercentricproperty; a two-dimensional imaging element that images an image of theimaging object focused by the imaging optical system; a mover thatrelatively integrally moves the imaging optical system and thetwo-dimensional imaging element with respect to the imaging object in adirection orthogonal to an optical axis of the imaging optical system;an illuminator that illuminates the imaging object from a side oppositeto the imaging optical system across the sample container held by theholder; and a controller that controls the two-dimensional imagingelement, the mover and the illuminator, wherein: the illuminatorincludes a plurality of illumination optical systems that has mutuallydifferent exit pupil positions and coaxially emit lights toward theimaging object; the controller causes one of the plurality ofillumination optical systems to emit light and causes thetwo-dimensional imaging element to image the imaging object when arelative position of the imaging optical system with respect to theimaging object reaches any one of a plurality of imaging positionsdetermined in advance while causing the mover to relatively move theimaging optical system and the two-dimensional imaging element withrespect to the imaging object; and the illumination optical system foremitting the light is switched according to the imaging position.

According to a second aspect of the disclosure, there is provided animaging method that images a raw sample as an imaging object carriedtogether with liquid in a sample container with a bottom surface havingoptical transparency. The method comprises: arranging an imaging opticalsystem having an object-side hypercentric property and a two-dimensionalimaging element for imaging an image of the imaging object focused bythe imaging optical system to face the sample container and arranging anilluminator for illuminating the imaging object on a side opposite tothe imaging optical system across the sample container; moving theimaging optical system and the two-dimensional imaging element withrespect to the imaging object, relatively; and imaging the imagingobject by the two-dimensional imaging element and emitting light fromthe illuminator when a relative position of the imaging optical systemwith respect to the imaging object reaches any one of a plurality ofimaging positions determined in advance, wherein: the illuminatorincludes a plurality of illumination optical systems having mutuallydifferent exit pupil positions, emitted lights propagating toward theimaging object being coaxial with each other; and light is emittedselectively from one of the plurality of illumination optical systemsand the illumination optical system for emitting the light is switchedaccording to the imaging position in the imaging step.

In the invention thus configured, an image of an area of the imagingobject including an area with the influence of meniscus can be imagedwith good image quality as with the technique described in JP2015-118036A by using the imaging optical system having the object-sidehypercentric property. More microscopically, refraction by the meniscusis strongly present, for example, near a peripheral edge part of thesample container, whereas that influence is hardly present, for example,in a central part of the sample container. In this way, the presence ofthe influence of the meniscus differs depending on positions. Directionsof chief rays of illumination light to be incident on the imaging objectcan be changed by providing the plurality of illumination opticalsystems having different exit pupil positions and switching them. Thus,imaging with the influence of the meniscus suppressed can be performedto correspond to a difference in the magnitude of refraction by themeniscus by switching the illumination optical systems according to theimaging position.

The above and further objects and novel features of the invention willmore fully appear from the following detailed description when the sameis read in connection with the accompanying drawing. It is to beexpressly understood, however, that the drawing is for purpose ofillustration only and is not intended as a definition of the limits ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a schematic configuration of one embodimentof an imaging apparatus according to the invention.

FIG. 2 is a diagram showing detailed configurations and ray diagrams ofthe illumination optical systems.

FIGS. 3A and 3B are diagrams showing illumination lights emitted fromthe first and second illumination optical systems.

FIGS. 4A and 4B are diagrams showing a state at the time of imaging thewell.

FIGS. 5 and 6 are diagrams showing a state of imaging when the size ofthe well is larger than that of the imaging field of view.

FIG. 7 is a diagram showing imaging using the second illuminationoptical system.

FIGS. 8A and 8B are diagrams illustrating a method for dividing one wellinto a plurality of images.

FIG. 9 is a flow chart showing an imaging process in this embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a diagram showing a schematic configuration of one embodimentof an imaging apparatus according to the invention. This imagingapparatus is an apparatus for imaging raw samples such as cells, cellcolonies and bacteria (hereinafter, referred to as “cells and the like”)cultured in liquid poured into recesses called wells W formed on theupper surface of a well plate WP.

The well plate WP is generally used in the fields of drug discovery andbioscience. The well plate WP has a flat plate shape and a plurality oftubular wells W having openings on the upper surface of this plate arearranged on the well plate WP. Each well W has, for example, asubstantially circular cross-section and a bottom surface is transparentand flat and has optical transparency. The cross-section and the bottomsurface shape of the well W are not limited to these. For example, thecross-section may be rectangular and the bottom surface may be curved.

The number of the wells W on the well plate WP is arbitrary. Forexample, a well plate WP having 96 (12×8 matrix array) wells can beused. A diameter and a depth of each well W are typically about severalmm. Note that the size of a well plate and the number of wells used inthis imaging apparatus 1 are arbitrary without being limited to these.For example, well plates having 6 to 384 wells are generally used.Further, without limitation to well plates having a plurality of wells,this imaging apparatus 1 can be used, for example, also for imaging ofcells and the like cultured in a flat container called a dish.

A predetermined amount of liquid as a culture medium M is poured intoeach well of the well plate WP, and the cells and the like culturedunder predetermined culture conditions in this liquid are imagingobjects of this imaging apparatus 1. The culture medium M may be addedwith appropriate reagents or may be gelled after being poured into thewells W in a liquid state. As described later, in this imaging apparatus1, cells and the like cultured on the inner bottom surfaces of the wellsW can be, for example, imaging objects. About 50 to 200 microliters ofthe liquid is generally usually used.

The imaging apparatus 1 includes an illuminator 10 arranged in an upperpart of the apparatus 1, a holder 12 for holding the well plate WP belowthe illuminator 10, an imager 13 arranged below the holder 12 and acontroller 14 with a CPU 141 for controlling the operation of each ofthese parts. The holder 12 holds the well plate WP in a substantiallyhorizontal posture by being held in contact with a peripheral edge partof the lower surface of the well plate WP carrying samples together withthe medium M in each well W.

The illuminator 10 includes two light sources 101, 111. For example,white LEDs (Light Emitting Diodes) can be used as the light sources 101,111. Light emitted from the light source 111 is incident on a beamsplitter 104 via a collector lens 112. On the other hand, light emittedfrom the light source 101 has an optical path reflected by a reflectionmirror 102 and is incident on the beam splitter 104 via a collector lens103. A beam emitted from the beam splitter 104 has a propagationdirection changed to a (−Z) direction, i.e. a vertically downwarddirection by a reflection mirror 105 and is emitted downward via acondenser lens 106. The emitted light is incident on at least one well Wfrom above the well plate WP supported on the holder 12 to illuminateimaging objects in the well W.

As just described, in the illuminator 10 of this embodiment, twoillumination optical systems, i.e. a first illumination optical system100 using the light source 101 as a light source thereof and composed ofthe reflection mirror 102, the collector lens 103, the beam splitter104, the reflection mirror 105, the condenser lens 106 and the like anda second illumination optical system 110 using the light source 111 as alight source thereof and composed of the collector lens 112, the beamsplitter 104, the reflection mirror 105, the condenser lens 106 and thelike coexist while sharing some constituent components.

The light sources 101, 111 are controlled to be turned on and off by alight source controller 146 provided in the controller 14 andselectively turned on in accordance with a control signal from the lightsource controller 146. Thus, the illuminator 10 can cause firstillumination light emitted from the first illumination optical system100 including the light source 101 and second illumination light emittedfrom the second illumination optical system 110 including the lightsource 111 to be selectively incident on the well W. The firstillumination light and the second illumination light are guided throughthe beam splitter 104 and these can be coaxially emitted. Specifically,center axes of the first illumination light and the second illuminationlight emitted from the condenser lens 106 coincide.

FIG. 2 is a diagram showing detailed configurations and ray diagrams ofthe illumination optical systems. In FIG. 2, the first and secondillumination optical systems 100, 110 sharing some constituentcomponents as described above are separately shown to clearly showoptical paths. Further, for the same purpose, the optical axes bent bythe reflection mirrors and the beam splitter is shown to be straight.Thus, the reflection mirrors 102, 105 and the beam splitter 104 having afunction of bending the optical axes are not shown.

In the first illumination optical system 100, light emitted from thelight source 101 is collected by the collector lens 103 and emittedtoward a sample surface, where the cells and the like as imaging objectsare present, via the condenser lens 106. The sample surface is a wellbottom surface Wb (see FIGS. 3A and 3B, etc.) in nocinal use. Thecollector lens 103 focuses an image of the light source 101 between thecollector lens 103 and the condenser lens 107. Specifically, a lightsource image C1 is formed between the collector lens 103 and thecondenser lens 106. Further, the collector lens 103 and the condenserlens 106 are arranged such that the light source image C1 is located ata front (light source-side) focus position of the condenser lens 106 andchief rays propagating from the condenser lens 106 toward the samplesurface are parallel to an optical axis shown by a chain line.Specifically, the first illumination optical system 100 constitutestelecentric illumination.

An aperture stop 107 is arranged on a light emitting surface of thelight source 101 if necessary to specify the size of the light sourceimage C1 formed by the collector lens 103. An NA (numerical aperture) ofillumination can be adjusted by the aperture stop 107. Further, a fieldstop 108 is arranged behind the collector lens 103 and before aconjugate point if necessary. In this way, only a range necessary forimaging can be illuminated to prevent the occurrence of flare in theimaging optical system.

In the second illumination optical system 110, light emitted from thelight source 111 is collected by the collector lens 112 and emittedtoward the sample surface via the condenser lens 106. The collector lens112 is imparted with such a refraction characteristic that a lightsource image C2 of the light source 111 is located behind the condenserlens 106 and before the sample surface.

An aperture stop 113 is arranged on a light emitting surface of thelight source 111 if necessary to specify the size of the light sourceimage C2 formed by the collector lens 112 and the condenser lens 106. AnNA of illumination can be adjusted by the aperture stop 113. Further, afield stop 114 is arranged between the collector lens 112 and thecondenser lens 106 if necessary. In this way, only a range necessary forimaging can be illuminated to prevent the occurrence of flare in theimaging optical system.

The two illumination optical systems 100, 110 share the condenser lens106. The beam splitter 104 for enabling this is provided between thecollector lenses and the condenser lenses of the illumination opticalsystems 100, 110. More specifically, the beam splitter 104 is arrangedat a position to satisfy conditions that the beam splitter 104 is behindthe collector lens 103 (field stop 108 if the field stop 108 isprovided) and before the condenser lens 106 in the first illuminationoptical system 100 and behind the collector lens 112 (field stop 114 ifthe field stop 114 is provided) and before the condenser lens 106 in thesecond illumination optical system 110.

Referring back to FIG. 1, the description of the imaging apparatus 1 iscontinued. The imager 13 for imaging the imaging objects such as cellsand the like in the wells W is provided below the well plate WP held bythe holder 12. In the imager 13, an objective lens 131 is arranged at aposition right below the well plate WP. An optical axis of the objectivelens 131 extends in a vertical downward direction and is coaxial withthe optical axes of the first and second illumination optical systems100, 110. Light emitted from the illuminator 10 and incident on theliquid surface from above the well W illuminates the imaging objects andlight transmitted downward from the bottom surface of the well W isincident on the objective lens 131. A low magnification afocal system132 and a high magnification afocal system 133 are switchably providedbelow the objective lens 131.

Specifically, the low magnification afocal system 132 and the highmagnification afocal system 133 are integrally movable in a horizontaldirection by an unillustrated drive mechanism, and one thereof isselectively positioned at a position right below the objective lens 131.In a state where the high magnification afocal system 133 is positionedat the position right below the objective lens 131 as shown in solidline in FIG. 1, a high magnification imaging optical system includingthe objective lens 131 and the high magnification afocal system 133 isconfigured. At this time, a relatively narrow range of the imagingobjects can be imaged at a high magnification. On the other hand, in astate where the low magnification afocal system 132 is positioned at theposition right below the objective lens 131 as shown in dotted line inFIG. 1, a low magnification imaging optical system including theobjective lens 131 and the low magnification afocal system 132 isconfigured. At this time, a relatively wide range of the imaging objectscan be imaged at a low magnification.

Light emitted from the low magnification afocal system 132 or the highmagnification afocal system 133 is reflected by a reflecting mirror 134and incident on an imaging element 136 via a focusing lens 135. Asdescribed later, the imaging optical system composed of the objectivelens 131, the low magnification afocal system 132, the focusing lens 135and the like has an object-side hypercentric optical property. On theother hand, the imaging optical system composed of the objective lens131, the high magnification afocal system 133, the focusing lens 135 andthe like has an object-side telecentric optical property.

The imaging element 136 is an area image sensor having a two-dimensionallight receiving surface and a CCD sensor or a CMOS sensor can be, forexample, used. An image of imaging objects focused on the lightreceiving surface of the imaging element 136 by the focusing lens 135 isimaged by the imaging element. The imaging element 136 converts thereceived optical image into an electrical signal and outputs it as animage signal. In such an imaging method, cells and the like as theimaging objects can be imaged in a non-contact, non-destructive andnon-invasive manner and damage on the cells and the like by imaging canbe suppressed. The operation of each part of the imager 13 is controlledby an imaging controller 143 provided in the controller 14.

The image signal output from the imaging element 136 is send to thecontroller 14. Specifically, the image signal is input to an ADconverter (A/D) 144 provided in the controller 14 and converted intodigital image data. The CPU 141 performs appropriate image processingsbased on the received image data. The controller 14 further includes animage memory 147 for storing and saving image data and a memory 148 forstoring and saving programs to be executed by the CPU 141 and datagenerated by the CPU 141, but these may be integrated. Further, theimage memory 147 and the memory 148 may be realized by appropriatelycombining a high-capacity storage and a semiconductor memory. The CPU141 performs various imaging processings and arithmetic processings byexecuting a control program stored in the memory 148 and operating eachpart of the apparatus.

The imager 13 is moved in the horizontal and vertical directions by amechanism controller 145 provided in the controller 14. Specifically,the mechanism controller 145 operates a drive mechanism 15 based on acontrol command from the CPU 141 to move the imager 13 in the horizontaldirection, whereby the imager 13 moves in the horizontal directionrelative to the wells W. Further, focusing is performed by moving theimager 13 in the vertical direction. When imaging is performed with onewell W entirely contained in an imaging field of view, the mechanismcontroller 145 positions the imager 13 in the horizontal direction suchthat the optical axis of the objective lens 131 coincides with a centerof this well W.

Further, the drive mechanism 15 relatively moves the illuminator 10integrally with the imager 13 as shown by dotted line arrows in FIG. 1when the imager 13 is moved in the horizontal direction. Specifically,the illuminator 10 is arranged such that a center of emitted lightsubstantially coincides with the optical axis of the objective lens 131.When the imager 13 moves in the horizontal direction, the illuminator 10moves in conjunction with the imager 13. In this way, a center of a beamof light from the illuminator 10 is constantly located on the opticalaxis of the objective lens 131 regardless of which well W is to beimaged, wherefore imaging conditions can be maintained to besatisfactory by making illumination conditions constant for each well W.

Besides, the controller 14 is provided with an interface (IF) unit 142.The interface unit 142 has a function of performing data exchange withan external apparatus connected via a communication line besides a userinterface function of receiving an operation input from a user andpresenting information such as processing results to the user. Althoughnot shown, an input receiver for receiving the operation input from theuser and a display for displaying and outputting a message, a processingresult and the like from the user are connected to the interface unit142 to realize the user interface function.

Note that the configuration of the controller 14 mentioned here isbasically the same as that of a general computer device. Accordingly,the controller 14 provided in the imaging apparatus 1 may be a dedicateddevice with the hardware described above or may be a general-purposeprocessing device such as a personal computer or a work stationincorporated with a control program for realizing a processing functionto be described later. Specifically, a general-purpose computer devicecan be utilized as the controller 14 of this imaging apparatus 1. In thecase of using the general-purpose computer device, it is sufficient toprovide the imaging apparatus 1 with control functions minimum necessaryto operate each part such as the imager 13.

FIGS. 3A and 3B are diagrams showing illumination lights emitted fromthe first and second illumination optical systems. More specifically,FIG. 3A shows first illumination light L1 emitted from the firstillumination optical system 100 and FIG. 3B shows second illuminationlight L2 emitted from the second illumination optical system 110. Asshown in FIG. 3A, the first illumination light L1 emitted from thecondenser lens 106 in the first illumination optical system 100 usingthe light source 101 as a light source is incident in a state wherechief rays are incident in a parallel state on the bottom surface Wb ofthe well W as the sample surface on which the imaging objects aredistributed. Specifically, the first illumination optical system 100constitutes telecentric illumination whose exit pupil position is atinfinity.

On the other hand, the second illumination light L2 emitted from thecondenser lens 106 in the second illumination optical system 110 usingthe light source 111 as a light source propagates in a direction towardthe optical axis of the second illumination optical system 110 andintersects with the optical axis above the well bottom surface Wb, i.e.on a front side when viewed from the illumination optical system.Specifically, an exit pupil position Pp where an image of the lightsource 111 (more strictly, aperture stop 113) is focused on the opticalpath of the second illumination optical system L2 is located at aposition closer than the well bottom surface Wb as the sample surface onwhich the imaging objects are distributed when viewed from the secondillumination optical system 110.

More specifically, under illumination by the second illumination opticalsystem 110, the image of the light source 111 is focused between anoutput end of the condenser lens 106 emitting the illumination light L2and the objective lens 131 of the imaging optical system. That is, aconjugate point for the light source 111 is located at this position.The holder 12 holds the well plate WP such that the well bottom surfaceWb as the sample surface on which the imaging objects are distributed islocated between this conjugate point and the objective lens 131. Thus, achief ray of the illumination light incident on the well bottom surfaceWb has a direction component in a direction away from the optical axesof the second illumination optical system 110 and the objective lens131. In the second illumination optical system 110, the exit pupilposition, the position of the image of the light source 111 and theposition of the conjugate point for the light source 111 coincide.

As just described, the exit pupil positions differ from each other inthe two illumination optical systems 100, 110 and these are properlyused according to need in imaging the well W as described later. Notethat stroboscopic illumination is used in imaging. That is, theillumination light is emitted only for a short time when imaging by theimager 13 is performed. Thus, the light source controller 146 canrealize the switch of the illumination light by selecting which of thetwo light sources 101, 111 is to be turned on. A specific mode ofproperly using one of these illumination optical systems 100, 110 isdescribed below.

FIGS. 4A and 4B are diagrams showing a state at the time of imaging thewell. More specifically, FIG. 4A is a diagram showing a propagation pathof light at the time of imaging the well and FIG. 4B is a diagramshowing a relationship of the well and the imaging field of view. Themedium M poured in a liquid state is in the well W carrying the cellsand the like as the imaging objects. Thus, the illumination light Lincident from above the well W is incident on the well bottom surface Wb(sample surface), where the imaging objects are present, via the liquidsurface of the medium M. The liquid surface generally forms an upwardconcave meniscus, whereby the illumination light L is refracted and bentoutwardly from the center of the well W. Refraction is small near thecenter of the well W and becomes larger toward the peripheral edge partof the well W.

The imaging optical system including the objective lens 131 constitutesan object-side hypercentric optical system and has a function ofefficiently collecting the light bent outwardly in this way and guidingit to the imaging element 136. Specifically, light incident obliquelyoutwardly can be focused on the imaging element 136 at a positiondistant from the optical axis of the lens. Thus, this imaging opticalsystem is suitable when one well W is imaged while being entirelycontained in an imaging field of view V as shown in FIG. 4B. This pointis as disclosed also in JP 2015-118036A.

One well W can be entirely contained in the imaging field of view V asshown in FIG. 4B when the well W having a relatively small openingdiameter is imaged at a low magnification. On the other hand, such as inthe case of imaging imaging objects carried in a well having a largeopening diameter (e.g. well on a well plate with six wells), the size ofan area to be imaged becomes relatively larger than that of the imagingfield of view and it may not be possible to contain the entire well W inthe imaging field of view V.

FIGS. 5 and 6 are diagrams showing a state of imaging when the size ofthe well is larger than that of the imaging field of view. Morespecifically, FIG. 5 shows imaging when the well peripheral edge part isnot contained in the imaging field of view and FIG. 6 shows imaging whenthe well peripheral edge part is contained in the imaging field of view.Here is described a case where the well W having a larger openingdiameter than that described thus far is imaged at a low magnification.For example, a similar way of thinking can be applied when the size ofan area to be imaged is larger than that of the imaging field of view Vsuch as when imaging objects carried in a shallow container having alarge opening diameter called a dish are imaged.

When the area to be imaged is wider than the imaging field of view V, itis considered to generate an image representing the entire area to beimaged by imaging and dividing this area into a plurality of images andcombining those images by image processings. In this case, theindividual images before synthesis need to have better quality to ensuredesired image quality of the generated image. Points of concern for thisare described next.

When the imaging field of view V contains only a central area distantfrom a peripheral edge part Wp of the well W as shown in FIG. 5, theinfluence of the meniscus on the surface of the medium M on the opticalpath is sufficiently small. Thus, in telecentric illumination, lightincident near the optical axis of the objective lens 131 is collectedand incident on the imaging element 136, whereas a mismatch occurs dueto a difference in inclination between the incident light and the chiefrays of the optical system at positions distant from the optical axis.

Specifically, at the positions distant from the optical axis, lightwhose chief rays are inclined outwardly as shown in dotted line in FIG.5 is received, assuming refraction on the liquid surface on the side ofthe objective lens 131, whereas the light transmitted through the well Wpropagates straight without being subjected to refraction by themeniscus, wherefore the inclinations of the chief rays in the incidentlight and those of the chief rays on a light receiving side do notcoincide. How the image looks may change due to this, particularly dueto the degradation of image quality in the peripheral edge part of theimaging field of view V, specifically due to a dark image or theincidence of the illumination light only in partial directions of alight collection range of the objective lens.

On the other hand, when the imaging field of view V is set in an areaincluding the peripheral edge part Wp of the well W or an area veryclose to this as shown in FIG. 6, the inclinations of the chief rays ofthe light refracted by the meniscus and those of the chief rays on thelight receiving side substantially coincide and light can be efficientlycollected near the well peripheral edge part Wp. Contrary to this, in apart near the well central part on a side opposite to the wellperipheral edge part Wp across the optical axis of the objective lens131, image quality is, of course, degraded since the light propagatingstraight is incident on the objective lens 131 having the inclinationsof the chief rays assuming refraction by the meniscus as in the case ofFIG. 5.

If an area capable of ensuring necessary image quality out of thephysical imaging field of view V of the imager 13 is considered to be aneffective imaging field of view, the effective imaging field of viewbecomes narrower when the area in the imaging field of view is notaffected by the meniscus as described above in the combination oftelecentric illumination and the hypercentric imaging optical system.Accordingly, in this embodiment, the second illumination optical system110 capable of obtaining good image quality in the absence of theinfluence of the meniscus is provided separately from the firstillumination optical system 100 constituting telecentric illumination.

FIG. 7 is a diagram showing imaging using the second illuminationoptical system. As described above, the illumination light L2 emittedfrom the condenser lens 106 in the second illumination optical system110 is such that the chief rays are inclined in the directions towardthe optical axis. Thus, in the absence of the influence of the meniscus,the chief rays of the illumination light incident on the bottom surfaceWb of the well W are not parallel to each other. Since the exit pupilposition Pp of the second illumination optical system 110 is locatedbefore the well bottom surface Wb when viewed from the secondillumination optical system 110 in this embodiment, the chief raysspread outwardly from the optical axis of the objective lens 131 in theillumination light L2 incident on the well bottom surface Wb.

If the inclinations of the chief rays at this time are set to coincidewith those of the chief rays on the side of the objective lens 131, thelight transmitted through the well bottom surface Wb is collected by theobjective lens 131 and finally guided to the imaging element 136 asshown in FIG. 7. Thus, imaging can be performed with good image qualityin the entire imaging field of view V and the entire physical imagingfield of view V can be utilized as the effective imaging field of view.

In terms of adjusting an incident direction of the illumination light inaccordance with the properties of the imaging optical system, it is, inprinciple, possible to obtain similar effects, for example, by arranginga point light source at the exit pupil position of the objective lens131. However, this is not realistic since problems such as theinterference of the light source and the well plate WP and thealteration of the samples due to heat emitted from the light source mayoccur due to the necessity to arrange the point light source at aposition right above the sample surface.

If the above illumination is constituted by the illumination opticalsystem for relaying the light emitted from the light source 111 by aplurality of lenses as in the above embodiment, it is possible torealize an illumination optical system optimized according to theproperties of the imaging optical system by appropriately combining thelenses, the stops and the like. For example, if the conjugate point ofthe light source 111 in the illumination optical system 110 and the exitpupil position of the objective lens 131 are set to coincide, theillumination light propagating in the direction away from the opticalaxis beyond the conjugate point can be efficiently guided to the imagingelement 136 by the objective lens 131.

As just described, in the imaging apparatus 1 of this embodiment, thefirst illumination optical system 100 suitable for imaging the areasubjected to the influence of the meniscus and the second illuminationoptical system 110 suitable for imaging the area free from the influenceof the meniscus are equipped as the illumination optical systems to becombined with the imaging optical system having the hypercentricproperty. When it is necessary to image an area wider than the imagingfield of view V of the imager 13, a plurality of images are imaged byproperly using the illumination optical systems for the areas with andwithout the influence of the meniscus, whereby the quality of an imageobtained by combining these images can be made satisfactory.

FIGS. 8A and 8B are diagrams illustrating a method for dividing one wellinto a plurality of images. More specifically, FIG. 8A shows an exampleof allocating images in dividing the well W into a plurality of imagesand FIG. 8B is a diagram showing a scanning path of the imager 13 toobtain such images. In FIG. 8A, each of the plurality of images coveringthe entire well W by partially overlapping each other is shown by asolid-line rectangle, diagonals of each rectangle are shown in dottedline and a centroid position thereof is shown by a black circle to makethe plurality of rectangles easily distinguishable. The centroidposition of the rectangle corresponds to a position where the opticalaxis of the objective lens 131 intersects with the well bottom surfaceWb during imaging.

In the allocation example shown in FIG. 8A, the entire well W is dividedinto eleven images. In the central part of the well W, the arrangementof the image is set not to include the well peripheral edge part Wp inthe imaging field of view. The image not including the well peripheraledge part Wp in this way is supposed to be imaged using the secondillumination optical system 110. On the other hand, the image imaged toinclude the well peripheral edge part Wp in the imaging field of view isarranged such that at least a centroid of the image is located in thewell W. Imaging is supposed to be performed using the first illuminationoptical system 100. By doing so, a difference in the inclinations of thechief rays can be reduced between the illumination side and the lightreceiving side at an outer side of the centroid position (side close tothe well peripheral edge part Wp) and image quality degradation can besuppressed.

FIG. 8B shows an example of a movement path of the imager 13 in dividingand imaging the well W into the plurality of images. In the imagingapparatus 1 of this embodiment, the imager 13 and the illuminator 10integrally horizontally move relative to the well plate WP placed on theholder 12. The plurality of images shown in FIG. 8A can be obtained byperforming imaging at appropriate relative positions while moving theimager 13 in the X and Y directions along the bottom surface of the wellplate WP. FIG. 8B shows the scanning movement path of the imager 13 atthis time, more precisely a locus of the intersection of the opticalaxis of the objective lens 131 provided in the imager 13 and the wellbottom surface Wb.

Points P1 to P11 indicated by black circles respectively correspond tothe centroid positions of the plurality of images shown in FIG. 8A.Further, since the centroid position of each image is also the positionof the optical axis of the objective lens 131 when this image is imaged,necessary images can be obtained by a series of scanning movements if ascanning movement recipe of the imager 13 (and the illuminator 10) isprepared such that the optical axis of the objective lens 131successively passes through these points P1 to P11 and imaging by theimager 13 is performed when the optical axis position of the objectivelens 131 reaches these points P1 to P11. In this sense, the positions ofthe imager 13 corresponding to the points P1 to P11 are referred to as“imaging positions”. If the allocation of the images is determined, theimaging positions can be set according to that. Further, Ps and Pedenote a start point and an end point of the optical axis position ofthe objective lens 131 in the scanning movement of the imager 13,respectively.

FIG. 9 is a flow chart showing an imaging process in this embodiment.The CPU 141 performs the imaging process shown in FIG. 9 by causing eachpart of the apparatus to perform a predetermined operation based on thecontrol program prepared in advance, whereby a plurality of images, forexample, shown in FIG. 8A are obtained. First, the imager 13 ispositioned at a predetermined start position by the drive mechanism 15that operates according to a control command from the mechanismcontroller 145 (Step S101). The start point Ps shown in FIG. 8Bcorresponds to the optical axis position of the objective lens 131 atthis time. Note that although only the scanning movement of the imager13 is described here, the illumination light 10 also moves according tothe movement of the imager 13 such that the center of the illuminationlight and the optical axis of the objective lens 131 constantly coincideas described above.

Subsequently, the scanning movement of the imager 13 relative to thewell W is started based on the scanning movement recipe set in advance(Step S102). When the imager 13 reaches an end position corresponding tothe end point Ps, the process is finished (Step S103). Until the endposition is reached, Steps S105 to S107 are performed for imaging everytime the imager 13 reaches any one of the imaging positionscorresponding to the points P1 to P11 (Step S104). At which position theimager 13 is located can be detected, for example, based on an outputsignal from a position sensor (not shown) mounted in the imager 13.

Specifically, the illumination optical system is selected according tothe imaging position where the imager 13 is currently located (StepS105). Specifically, the first illumination optical system 100 isselected if the well peripheral edge part Wp is included in the imagingfield of view V at the current position of the imager 13 and the secondillumination optical system 110 is selected if the well peripheral edgepart Wp is not included. In the example shown in FIGS. 8A and 8B, thesecond illumination optical system 110 is selected at the imagingpositions corresponding to the points P5 to P7 and the firstillumination optical system 100 is selected at the imaging positionscorresponding to the other points P1 to P4 and P8 to P11. As justdescribed, the selective arrangement of the illumination optical systems100, 110 corresponds to an example of an “arranging step” of theinvention.

Subsequently, the imaging objects are stroboscopically illuminated bylighting the light source of the selected illumination optical systemfor a predetermined time and, simultaneously with this, the imagingelement 136 performs imaging, whereby one image is obtained (Step S106:imaging step). Image data obtained by digitizing an image signal outputfrom the imaging element 136 by the AD converter 144 is stored in theimage memory 147 (Step S107). By repeating the above process until theimager 13 reaches the end position, imaging is performed at the imagingposition corresponding to each of the points P1 to P11 and eleven imagesare obtained.

Since imaging is performed under stroboscopic illumination, the scanningmovement of the imager 13 needs not be temporarily stopped for imagingand the drive mechanism 15 may scan and move the imager 13 at a constantspeed in accordance with the scanning movement recipe. By optimizing thescanning movement recipe to minimize a length of the path connecting therespective points P1 to P11, a time required for imaging can beshortened.

Out of the plurality of images thus obtained, those including the wellperipheral edge part Wp are imaged under illumination by the firstillumination optical system and those not including the well peripheraledge part Wp are imaged under illumination by the second illuminationoptical system 110. Thus, in each image, a reduction of image qualitydue to the presence or absence of the meniscus and a mismatch with theillumination optical system is suppressed. The image of the entire wellW can be generated with good quality by extracting and combining partswith good image quality from the respective images. In an area where theplurality of images overlap, the image having better image quality maybe adopted in view of the position of this area in the well W and theused illumination optical system.

As described above, in this embodiment, two illumination optical systems100, 110 are provided. the illumination optical system 100 iscorresponding to the case where the influence of the meniscus is presentin the imaging field of view V of the imager 13 while the illuminationoptical system 110 is corresponding to the case free from the influenceof the meniscus. Imaging is performed while those illumination opticalsystems are switched according to the imaging position. By doing so,images with good image quality can be obtained in both the areas withthe influence of the meniscus and those without the influence of themeniscus out of the areas to be imaged.

As described above, in the imaging apparatus 1 of this embodiment, theilluminator 10 functions as an “illuminator” of the invention, theholder 12 functions as a “holder” of the invention, the controller 14functions as a “controller” of the invention and the drive mechanism 15functions as a “mover” of the invention. Further, the reflection mirror102, the collector lens 103, the beam splitter 104, the reflectionmirror 105 and the condenser lens 106 integrally function as one“illumination optical system” of the invention. Further, the collectorlens 112, the beam splitter 104, the reflection mirror 105 and thecondenser lens 106 integrally function as another “illumination opticalsystem” of the invention.

Further, the objective lens 131, the low magnification afocal system132, the high magnification afocal system 133, the reflection mirror 134and the focusing lens 135 integrally function as an “imaging opticalsystem” of the invention, and the imaging element 136 functions as a“two-dimensional imaging element” of the invention. Further, the wellplate WP corresponds to a “sample container” of the invention in theabove embodiment.

Note that the invention is not limited to the above embodiment andvarious changes other than those described above can be made withoutdeparting from the gist of the invention. For example, in theilluminator 10 of the above embodiment includes two illumination opticalsystems, i.e. the first illumination optical system 100 constitutingtelecentric illumination and having the exit pupil position at infinityand the second illumination optical system 110 having the exit pupilposition Pp before the well bottom surface Wb. However, the exit pupilpositions in the illumination optical systems are not limited to theseand it is sufficient to provide two or more illumination optical systemshaving different exit pupil positions. The effects are more remarkableas a difference between the exit pupil positions becomes larger.Further, three or more illumination optical systems may be provided. Forexample, an illumination optical system having a more limitedirradiation range may be further provided for high magnificationimaging.

Further, although two light sources 101, 111 are provided incorrespondence with the two illumination optical systems 100, 110 in theabove embodiment, two illumination optical systems may be configured bya single light source and two optical systems. Further, although some ofthe members constituting the two illumination optical systems are sharedin the above embodiment, completely independent two illumination opticalsystems may be provided.

Further, the allocation of the images in the above imaging process ismerely for description, and an actual arrangement is not limited tothis. Further, although the case of imaging only one well is describedin the above allocation example, the scanning movement recipe may be soconfigured that a plurality of wells can be collectively imaged by aseries of scanning movements.

As described above, according to the invention, imaging is performed byswitching a plurality of illumination optical systems having mutuallydifferent exit pupil positions, thus having mutually differentdirections of chief rays of illumination light incident on imagingobjects, according to an imaging position, whereby an image with goodimage quality can be obtained by suppressing the influence of meniscus.

Further, as described by way of the specific embodiment, one of theillumination optical systems may constitute telecentric illumination forcausing light to be incident on the imaging objects such that chief raysare parallel to an optical axis of an imaging optical system in theinvention. In such an illumination optical system, the inclinations ofthe chief rays approach those of the chief rays of the imaging opticalsystem having a hypercentric property by bending the chief raysoutwardly by refraction on a liquid surface, wherefore good imagequality can be obtained when the influence of the meniscus is present inthe imaging field of view.

In this case, the plurality of illumination optical systems may furtherinclude an illumination optical system whose exit pupil position islocated closer than the imaging objects when viewed from theillumination optical system. In such an illumination optical system,illumination light having inclinations equivalent to the inclinations ofthe chief rays of the imaging optical system having the hypercentricproperty can be caused to be incident on the imaging objects when notbeing subjected to the influence of the meniscus.

Further, for example, the lights emitted from the plurality ofillumination optical systems may be coaxial with the optical axis of theimaging optical system. If the emitted lights are coaxial with theoptical axis of the imaging optical system, the inclinations of thechief rays can be easily matched between the illumination optical systemand the imaging optical system at each position on and around theoptical axis.

Further, for example, the imaging field of view on the bottom surface ofthe sample container may be smaller than the bottom surface of thesample container. Even if the imaging field of view is smaller than thebottom surface of the sample container and the entire bottom surface ofthe sample container cannot be contained in the imaging field of view,the entire interior of the sample container can be imaged by dividingthe bottom surface into a plurality of images. In this case, theinfluence of the meniscus is possibly present or absent depending on theimaging position. In the invention, an image with good quality can beobtained both when the influence of the meniscus is present and when theinfluence of the meniscus is absent by switchingly using the pluralityof illumination optical systems. Thus, particularly remarkable effectscan be exhibited when an area to be imaged is divided and imaged into aplurality of images in this way.

Further, for example, the holder may hold the sample container in asubstantially horizontal posture, the illuminator may be arranged abovethe sample container held by the holder to illuminate the imagingobjects from above, and the two-dimensional imaging element may bearranged below the sample container held by the holder and performimaging by causing light incident from the illuminator via the liquidsurface and emitted from the bottom surface of the sample container tobe incident on the imaging optical system. According to such aconfiguration, the optical axis in a direction perpendicular to thesubstantially horizontal liquid surface can be set and each part of theapparatus is easily supported and positioned.

This invention can be suitably applied to imaging apparatuses forimaging various raw samples such as cells, cell colonies, spheroids,bacteria, lesion tissues and microorganisms.

Although the invention has been described with reference to specificembodiments, this description is not meant to be construed in a limitingsense. Various modifications of the disclosed embodiment, as well asother embodiments of the invention, will become apparent to personsskilled in the art upon reference to the description of the invention.It is therefore contemplated that the appended claims will cover anysuch modifications or embodiments as fall within the true scope of theinvention.

What is claimed is:
 1. An imaging apparatus that images a raw sample asan imaging object carried together with liquid in a sample containerwith a bottom surface having optical transparency, the apparatuscomprising: a holder that holds the sample container; an imaging opticalsystem, arranged to face the sample container held by the holder, thathas an object-side hypercentric property; a two-dimensional imagingelement that images an image of the imaging object focused by theimaging optical system; a mover that relatively integrally moves theimaging optical system and the two-dimensional imaging element withrespect to the imaging object in a direction orthogonal to an opticalaxis of the imaging optical system; an illuminator that illuminates theimaging object from a side opposite to the imaging optical system acrossthe sample container held by the holder; and a controller that controlsthe two-dimensional imaging element, the mover and the illuminator,wherein: the illuminator includes a plurality of illumination opticalsystems that has mutually different exit pupil positions and coaxiallyemit lights toward the imaging object; the controller causes one of theplurality of illumination optical systems to emit light and causes thetwo-dimensional imaging element to image the imaging object when arelative position of the imaging optical system with respect to theimaging object reaches any one of a plurality of imaging positionsdetermined in advance while causing the mover to relatively move theimaging optical system and the two-dimensional imaging element withrespect to the imaging object; and the illumination optical system foremitting the light is switched according to the imaging position.
 2. Theimaging apparatus according to claim 1, wherein one of the illuminationoptical systems constitute telecentric illumination for causing light,whose chief ray is parallel to the optical axis of the imaging opticalsystem, to be incident on the imaging object.
 3. The imaging apparatusaccording to claim 2, wherein the plurality of illumination opticalsystems include the one whose exit pupil position is closer than theimaging object when viewed from the illumination optical system.
 4. Theimaging apparatus according to claim 1, wherein lights emitted from theplurality of illumination optical systems are coaxial with the opticalaxis of the imaging optical system.
 5. The imaging apparatus accordingto claim 1, wherein an imaging field of view on the bottom surface ofthe sample container is smaller than the bottom surface of the samplecontainer.
 6. The imaging apparatus according to claim 1, wherein: theholder holds the sample container in a substantially horizontal posture;the illuminator is arranged above the sample container held by theholder and illuminates the imaging object from above; and thetwo-dimensional imaging element is arranged below the sample containerheld by the holder and performs imaging by causing light incident fromthe illuminator via a liquid surface of the liquid and emitted from thebottom surface of the sample container to be incident on the imagingoptical system.
 7. An imaging method that images a raw sample as animaging object carried together with liquid in a sample container with abottom surface having optical transparency, the method comprising:arranging an imaging optical system having an object-side hypercentricproperty and a two-dimensional imaging element for imaging an image ofthe imaging object focused by the imaging optical system to face thesample container and arranging an illuminator for illuminating theimaging object on a side opposite to the imaging optical system acrossthe sample container; moving the imaging optical system and thetwo-dimensional imaging element with respect to the imaging object,relatively; and imaging the imaging object by the two-dimensionalimaging element and emitting light from the illuminator when a relativeposition of the imaging optical system with respect to the imagingobject reaches any one of a plurality of imaging positions determined inadvance, wherein: the illuminator includes a plurality of illuminationoptical systems having mutually different exit pupil positions, emittedlights propagating toward the imaging object being coaxial with eachother; and light is emitted selectively from one of the plurality ofillumination optical systems and the illumination optical system foremitting the light is switched according to the imaging position in theimaging step.